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Question 7.1 A liquid is in equilibrium with its vapour in a sealed container at a fixed
temperature. The volume of the container is suddenly increased.
a) What is the initial effect of the change on vapour pressure?
b) How do rates of evaporation and condensation change initially?
c) What happens when equilibrium is restored finally and what will be the final
vapour pressure?
Question 7.2 What is Kc for the following equilibrium when the equilibrium concentration of
each substance is:
[SO2]= 0.60M, [O2] = 0.82M and [SO3] = 1.90M ?
2SO2(g) + O2(g) ƒ 2SO3(g)
Question 7.3 At a certain temperature and total pressure of 105Pa, iodine vapour contains 40%
by volume of I atoms
I2 (g) ƒ 2I(g)
Calculate Kp for the equilibrium.
Question 7.4 Write the expression for the equilibrium constant, Kc for each of the following
reactions:
(i) 2NOCl (g) ƒ 2NO (g) + Cl2 (g)
(ii) 2Cu(NO3)2 (s) ƒ 2CuO (s) + 4NO2 (g) + O2 (g)
(iii) CH3COOC2H5(aq) + H2O(l) ƒ CH3COOH (aq) + C2H5OH (aq)
(iv) Fe3+ (aq) + 3OH– (aq) ƒ Fe(OH)3 (s)
(v) I2 (s) + 5F2 ƒ 2IF5
Question 7.5 Find out the value of Kc for each of the following equilibria from the value of Kp:
(i) 2NOCl (g) ƒ 2NO (g) + Cl2 (g); Kp= 1.8 × 10–2 at 500 K
(ii) CaCO3 (s) ƒ CaO(s) + CO2(g); Kp= 167 at 1073 K
Question 7.6 For the following equilibrium, Kc= 6.3 × 1014 at 1000 K
NO (g) + O3 (g) ƒ NO2 (g) + O2 (g) Both the forward and reverse reactions in the equilibrium are elementary
bimolecular reactions. What is Kc, for the reverse reaction?
Question 7.7 Explain why pure liquids and solids can be ignored while writing the equilibrium
constant expression?
Question 7.8 Reaction between N2 and O2– takes place as follows:
2N2 (g) + O2 (g) ƒ 2N2O (g)
If a mixture of 0.482 mol N2 and 0.933 mol of O2 is placed in a 10 L reaction
vessel and allowed to form N2O at a temperature for which Kc= 2.0 × 10–37,
determine the composition of equilibrium mixture.
Question 7.9 Nitric oxide reacts with Br2 and gives nitrosyl bromide as per reaction given
below:
2NO (g) + Br2 (g) ƒ 2NOBr (g)
When 0.087 mol of NO and 0.0437 mol of Br2 are mixed in a closed container at
constant temperature, 0.0518 mol of NOBr is obtained at equilibrium. Calculate
equilibrium amount of NO and Br2 .
Question 7.10 At 450K, Kp= 2.0 × 1010/bar for the given reaction at equilibrium.
2SO2(g) + O2(g) ƒ 2SO3 (g)
What is Kc at this temperature ?
Question 7.11 A sample of HI(g) is placed in flask at a pressure of 0.2 atm. At equilibrium the
partial pressure of HI(g) is 0.04 atm. What is Kp for the given equilibrium ?
2HI (g) ƒ H2 (g) + I2 (g)
Question 7.12 A mixture of 1.57 mol of N2, 1.92 mol of H2 and 8.13 mol of NH3 is introduced into
a 20 L reaction vessel at 500 K. At this temperature, the equilibrium constant,
Kc for the reaction N2 (g) + 3H2 (g) ƒ 2NH3 (g) is 1.7 × 102. Is the reaction mixture
at equilibrium? If not, what is the direction of the net reaction?
Question 7.13 The equilibrium constant expression for a gas reaction is,
[ ][
[ ] [
4
3 2
4
2
NH O
NO H O
= c K
Write the balanced chemical equation corresponding to this expression.
Question 7.14 One mole of H2O and one mole of CO are taken in 10 L vessel and heated to
725 K. At equilibrium 40% of water (by mass) reacts with CO according to the
equation,
H2O (g) + CO (g) ƒ H2 (g) + CO2 (g)
Calculate the equilibrium constant for the reaction.
Question 7.15 At 700 K, equilibrium constant for the reaction:
H2 (g) + I2 (g) ƒ 2HI (g)
is 54.8. If 0.5 mol L–1 of HI(g) is present at equilibrium at 700 K, what are the
concentration of H2(g) and I2(g) assuming that we initially started with HI(g) and
allowed it to reach equilibrium at 700K?
Question 7.16 What is the equilibrium concentration of each of the substances in the
equilibrium when the initial concentration of ICl was 0.78 M ?
2ICl (g) ƒ I2 (g) + Cl2 (g); Kc = 0.14
Question 7.17 Kp = 0.04 atm at 899 K for the equilibrium shown below. What is the equilibrium
concentration of C2H6 when it is placed in a flask at 4.0 atm pressure and allowed
to come to equilibrium?
C2H6 (g) ƒ C2H4 (g) + H2 (g)
Question 7.18 Ethyl acetate is formed by the reaction between ethanol and acetic acid and the
equilibrium is represented as:
CH3COOH (l) + C2H5OH (l) ƒ CH3COOC2H5 (l) + H2O (l)
(i) Write the concentration ratio (reaction quotient), Qc, for this reaction (note:
water is not in excess and is not a solvent in this reaction)
(ii) At 293 K, if one starts with 1.00 mol of acetic acid and 0.18 mol of ethanol,
there is 0.171 mol of ethyl acetate in the final equilibrium mixture. Calculate
the equilibrium constant.
(iii) Starting with 0.5 mol of ethanol and 1.0 mol of acetic acid and maintaining
it at 293 K, 0.214 mol of ethyl acetate is found after sometime. Has equilibrium
been reached?
Question 7.19 A sample of pure PCl5 was introduced into an evacuated vessel at 473 K. After
equilibrium was attained, concentration of PCl5 was found to be
0.5 × 10–1 mol L–1. If value of Kc is 8.3 × 10–3, what are the concentrations of PCl3
and Cl2 at equilibrium?
PCl5 (g) ƒ PCl3 (g) + Cl2(g)
Question 7.20 One of the reaction that takes place in producing steel from iron ore is the
reduction of iron(II) oxide by carbon monoxide to give iron metal and CO2.
FeO (s) + CO (g) ƒ Fe (s) + CO2 (g); Kp = 0.265 atm at 1050K
What are the equilibrium partial pressures of CO and CO2 at 1050 K if the
initial partial pressures are: pCO= 1.4 atm and CO2 p =0.80 atm?
Question 7.21 Equilibrium constant, Kc for the reaction
N2 (g) + 3H2 (g) ƒ 2NH3 (g) at 500 K is 0.061
At a particular time, the analysis shows that composition of the reaction mixture
is 3.0 mol L–1 N2, 2.0 mol L–1 H2 and 0.5 mol L–1 NH3. Isthe reaction at equilibrium?
If not in which direction does the reaction tend to proceed to reach equilibrium?
Question 7.22 Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches
the equilibrium:
2BrCl (g) ƒ Br2 (g) + Cl2 (g)
for which Kc= 32 at 500 K. If initially pure BrCl is present at a concentration of
3.3 × 10–3 mol L–1, what is its molar concentration in the mixture at equilibrium?
Question 7.23 At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO2 in equilibrium
with soild carbon has 90.55% CO by mass
C (s) + CO2 (g) ƒ 2CO (g)
Calculate Kc for this reaction at the above temperature.
Question 7.24 Calculate a) ΔG0 and b) the equilibrium constant for the formation of NO2 from
NO and O2 at 298K
NO (g) + ½ O2 (g) ƒ NO2 (g)
where
ΔfG0 (NO2) = 52.0 kJ/mol ΔfG0 (NO) = 87.0 kJ/mol
ΔfG0 (O2) = 0 kJ/mol
Question 7.25 Does the number of moles of reaction products increase, decrease or remain
same when each of the following
equilibria is subjected to a decrease in pressure
by increasing the volume?
(a) PCl5 (g) ƒ PCl3 (g) + Cl2 (g)
(b) CaO (s) + CO2 (g) ƒ CaCO3 (s)
(c) 3Fe (s) + 4H2O (g) ƒ Fe3O4 (s) + 4H2 (g)
Question 7.26 Which of the following reactions will get affected by increasing the pressure?
Also, mention whether change will cause the reaction to go into forward or
backward direction.
(i) COCl2 (g) ƒ CO (g) + Cl2 (g)
(ii) CH4 (g) + 2S2 (g) ƒ CS2 (g) + 2H2S (g)
(iii) CO2 (g) + C (s) ƒ 2CO (g)
(iv) 2H2 (g) + CO (g) ƒ CH3OH (g
)
(v) CaCO3 (s) ƒ CaO (s) + CO2 (g)
(vi) 4 NH3 (g) + 5O2 (g) ƒ 4NO (g) + 6H2O(g)
Question 7.27 The equilibrium constant for the following reaction is 1.6 ×105 at 1024K
H2(g) + Br2(g) ƒ 2HBr(g)
Find the equilibrium pressure of all gases if 10.0 bar of HBr is introduced into a
sealed container at 1024K.
Question28 Dihydrogen gas is obtained from natural gas by partial oxidation with steam as
per following endothermic reaction: CH4 (g) + H2O (g) ƒ CO (g) + 3H2 (g)
(a) Write as expression for Kp for the above reaction.
(b) How will the values of Kp and composition of equilibrium mixture be affected
by
(i) increasing the pressure
(ii) increasing the temperature
(iii) using a catalyst ?
Question 7.29 Describe the effect of :
a) addition of H2
b) addition of CH3OH
c) removal of CO
d) removal of CH3OH
on the equilibrium of the reaction:
2H2(g) + CO (g) ƒ CH3OH (g)
Question 7.30 At 473 K, equilibrium constant Kc for decomposition of phosphorus pentachloride,
PCl5 is 8.3 ×10-3. If decomposition is depicted as,
PCl5 (g) ƒ PCl3 (g) + Cl2 (g) ΔrH0 = 124.0 kJ mol–1
a) write an expression for Kc for the reaction.
b) what is the value of Kc for the reverse reaction at the same temperature ?
c) what would be the effect on Kc if
(i) more PCl5 is added
(ii) pressure is increased
(iii) the temperature is increased ?
Question 7.31 Dihydrogen gas used in Haber’s process is produced by reacting methane from
natural gas with high temperature steam. The first stage of two stage reaction
involves the formation of CO and H2. In second stage, CO formed in first stage is
reacted with more steam in water gas shift reaction,
CO (g) + H2O (g) ƒ CO2 (g) + H2 (g)
If a reaction vessel at 400 °C is charged with an equimolar mixture of CO and
steam such that CO H2O p = p = 4.0 bar, what will be the partial pressure of H2 at
equilibrium? Kp= 10.1 at 400°C
Question 7.32 Predict which of the following reaction will have appreciable concentration of
reactants and products:
a) Cl2 (g) ƒ 2Cl (g) Kc = 5 ×10–39
b) Cl2 (g) + 2NO (g) ƒ 2NOCl (g) Kc = 3.7 × 108
c) Cl2 (g) + 2NO2 (g) ƒ 2NO2Cl (g) Kc = 1.8
Question 7.33 The value of Kc for the reaction 3O2 (g) ƒ 2O3 (g) is 2.0 ×10–50 at 25°C. If the
equilibrium concentration of O2 in air at 25°C is 1.6 ×10–2, what is the
concentration of O3?
Question 7.34 The reaction, CO(g) + 3H2(g) ƒ CH4(g) + H2O(g)
is at equilibrium at 1300 K in a 1L flask. It also contain 0.30 mol of CO, 0.10 mol
of H2 and 0.02 mol of H2O and an unknown amount of CH4 in the flask. Determine
the concentration of CH4 in the mixture. The equilibrium constant, Kc for the
reaction at the given temperature is 3.90.
Question 7.35 What is meant by the conjugate acid-base pair? Find the conjugate acid/base
for the following species:
HNO2, CN–, HClO4, F –, OH–, CO3
2–, and S2–
Question 7.36 Which of the followings are Lewis acids? H2O, BF3, H+, and NH4
+ 7.37 What will be the conjugate bases for the Brönsted acids: HF, H2SO4 and HCO3? 7.38 Write the conjugate acids for the following Brönsted bases: NH2
–, NH3 and HCOO–.
Question 7.39 The species: H2O, HCO3
–, HSO4
– and NH3 can act both as Brönsted acids and
bases. For each case give the corresponding conjugate acid and base.
Question 7.40 Classify the following species into Lewis acids and Lewis bases and show how
these act as Lewis acid/base:
(a) OH–
(b) F–
(c) H+
(d) BCl3 .
Question 7.41 The concentration of hydrogen ion in a sample of soft drink is 3.8 × 10–3 M. what
is its pH?
Question 7.42 The pH of a sample of vinegar is 3.76. Calculate the concentration of hydrogen
ion in it.
Question 7.43 The ionization constant of HF, HCOOH and HCN at 298K are 6.8 × 10–4,
1.8 × 10–4 and 4.8 × 10–9 respectively. Calculate the ionization constants of the
corresponding conjugate base.
Question 7.44 The ionization constant of phenol is 1.0 × 10–10. What is the concentration of
phenolate ion in 0.05 M solution of phenol? What will be its degree of ionization
if the solution is also 0.01M in sodium phenolate?
Question 7.45 The first ionization constant of H2S is 9.1 × 10–8. Calculate the concentration of
HS– ion in its 0.1M solution. How will this concentration be affected if the solution is 0.1M in HCl also ? If the second dissociation constant of H2S is
1.2 × 10–13, calculate the concentration of S2– under both conditions.
Question 7.46 The ionization constant of acetic acid is 1.74 × 10–5. Calculate the degree of
dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of
acetate ion in the solution and its pH.
Question 7.47 It has been found that the pH of a 0.01M solution of an organic acid is 4.15.
Calculate the concentration of the anion, the ionization constant of the acid
and its pKa .
Question 7.48 Assuming complete dissociation, calculate the pH of the following solutions:
(a) 0.003 M HCl
(b) 0.005 M NaOH
(c) 0.002 M HBr
(d) 0.002 M KOH
Question 7.49 Calculate the pH of the following solutions:
a) 2 g of TlOH dissolved in water to give 2 litre of solution.
b) 0.3 g of Ca(OH)2 dissolved in water to give 500 mL of solution.
c) 0.3 g of NaOH dissolved in water to give 200 mL of solution.
d) 1mL of 13.6 M HCl is diluted with water to give 1 litre of solution.
Question 7.50 The degree of ionization of a 0.1M bromoacetic acid solution is 0.132. Calculate
the pH of the solution and the pKa of bromoacetic acid.
Question 7.51 The pH of 0.005M codeine (C18H21NO3) solution is 9.95. Calculate its ionization
constant and pKb.
Question 7.52 What is the pH of 0.001M aniline solution ? The ionization constant of aniline
can be taken from Table7. Calculate the degree of ionization of aniline in the
solution. Also calculate the ionization constant of the conjugate acid of aniline.
Question 7.53 Calculate the degree of ionization of 0.05M acetic acid if its pKa value is 4.74.
How is the degree of dissociation affected when its solution also contains
(a) 0.01M (b) 0.1M in HCl ?
Question 7.54 The ionization constant of dimethylamine is 5.4 × 10–4. Calculate its degree of
ionization in its 0.02M solution. What percentage of dimethylamine is ionized if
the solution is also 0.1M in NaOH?
Question 7.55 Calculate the hydrogen ion concentration in the following biological fluids whose
pH are given below:
(a) Human muscle-fluid, 6.83
(b) Human stomach fluid, 1.2
(c) Human blood,7.38
(d) Human saliva, 6.4.
Question 7.56 The pH of milk, black coffee, tomato juice, lemon juice and egg white are 6.8,
5.0, 4.2, 2.2 and 7.8 respectively. Calculate corresponding hydrogen ion
concentration in each.
Question 7.57 If 0.561 g of KOH is dissolved in water to give 200 mL of solution at 298 K.
Calculate the concentrations of potassium, hydrogen and hydroxyl ions. What
is its pH?
Question 7.58 The solubility of Sr(OH)2 at 298 K is 19.23 g/L of solution. Calculate the
concentrations of strontium and hydroxyl ions and the pH of the solution.
Question 7.59 The ionization constant of propanoic acid is 1.32 × 10–5. Calculate the degree of
ionization of the acid in its 0.05M solution and also its pH. What will be its
degree of ionization if the solution is 0.01M in HCl also?
Question 7.60 The pH of 0.1M solution of cyanic acid (HCNO) is 2.34. Calculate the ionization
constant of the acid and its degree of ionization in the solution.
Question 7.61 The ionization constant of nitrous acid is 4.5 × 10–4. Calculate the pH of 0.04 M
sodium nitrite solution and also its degree of hydrolysis.
Question 7.62 A 0.02M solution of pyridinium hydrochloride has pH = 3.44. Calculate the
ionization constant of pyridine.
Question 7.63 Predict if the solutions of the following salts are neutral, acidic or basic:
NaCl, KBr, NaCN, NH4NO3, NaNO2 and KF
Question 7.64 The ionization constant of chloroacetic acid is 1.35 × 10–3. What will be the pH of
0.1M acid and its 0.1M sodium salt solution?
Question 7.65 Ionic product of water at 310 K is 2.7 × 10–14. What is the pH of neutral water at
this temperature?
Question 7.66 Calculate the pH of the resultant mixtures:
a) 10 mL of 0.2M Ca(OH)2 + 25 mL of 0.1M HCl
b) 10 mL of 0.01M H2SO4 + 10 mL of 0.01M Ca(OH)2
c) 10 mL of 0.1M H2SO4 + 10 mL of 0.1M KOH
Question 7.67 Determine the solubilities of silver chromate, barium chromate, ferric hydroxide,
lead chloride and mercurous iodide at 298K from their solubility product
constants given in Table Determine also the molarities of individual ions.
Question 7.68 The solubility product constant of Ag2CrO4 and AgBr are 1.1 × 10–12 and
5.0 × 10–13 respectively. Calculate the ratio of the molarities of their saturated
solutions.
Question 7.69 Equal volumes of 0.002 M solutions of sodium iodate and cupric chlorate are
mixed together. Will it lead to precipitation of copper iodate? (For cupric iodate
Ksp = 4 × 10–8 ).
Question 7.70 The ionization constant of benzoic acid is 6.46 × 10–5 and Ksp for silver benzoate
is 2.5 × 10–13. How many times is silver benzoate more soluble in a buffer of pH
3.19 compared to its solubility in pure water?
Question 7.71 What is the maximum concentration of equimolar solutions of ferrous sulphate
and sodium sulphide so that when mixed in equal volumes, there is no
precipitation of iron sulphide? (For iron sulphide, Ksp = 6.3 × 10–18).
Question 7.72 What is the minimum volume of water required to dissolve 1g of calcium sulphate
at 298 K? (For calcium sulphate, Ksp is 9.1 × 10–6).
Question
7.73 The concentration of sulphide ion in 0.1M HCl solution saturated with hydrogen
sulphide is 1.0 × 10–19 M. If 10 mL of this is added to 5 mL of 0.04 M solution of
the following: FeSO4, MnCl2, ZnCl2 and CdCl2. in which of these solutions
precipitation will take place?
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